1. Field of the Invention
The present invention relates generally to devices for replenishing fixing solutions, particularly in connection with an automatic processor for processing film, particularly high contrast film suitable for a prepress process.
2. Description of the Related Art
An apparatus for developing high contrast film, and capable of performing high-temperature high-speed processing (so-called rapid access developing) has been recently developed. This apparatus employs a developing solution and a fixing solution suitable for rapid access developing.
A replenishing solution for suitably replenishing such developing and fixing solutions is prepared by mixing different chemicals (including a diluting solution) in a predetermined ratio. This is done according to a mixed replenishment method or a separate replenishment method. In the mixed replenishment method, the chemicals are mixed together and then used for replenishment. In the separate replenishment method, the chemicals are supplied separately.
In the separate replenishment method, there is no pre-mixing of the chemicals, and hence no degradation occurs. Further, when the chemicals are diluted with water, the water can be simply supplied by a water pipe located close to the apparatus. There is no need for a water tank, and the size of tanks for replenishing the other chemicals can be reduced. The separate replenishment method has many other practical merits, e.g., a large replenisher tank which is required in the mixed replenishment method becomes unnecessary. For the foregoing reasons, the separate replenishment method has become the preferred method.
A known developer replenishing device for performing the separate replenishment method is illustrated in FIG. 1. Different chemicals A, B and water C are supplied by constant rate pumps PA, PB and PC to a fixing tank 2. Thus, a fixing solution F is replenished in a predetermined mixing ratio. The constant rate pumps PA, PB and PC suck up chemicals A, B and water C from tanks 11A, 11B and 11C.
Chemical A is a so-called fixing agent containing thiosulfate (sodium thiosulfate Na.sub.2 S.sub.2 O.sub.3 and so on) as its principal component. Chemical B is a so-called hardening agent containing acid (acetic acid CH.sub.3 COOH and so on), alum and so on as its components.
Referring to FIG. 2, the pipes 12A, 12B and 12C (for the chemicals A, B and water C, respectively) are arranged such that their ends extend into the solution F in the fixing tank 2, i.e., the ends are located below the surface of the solution F.
In operation, the fixing solution (mother liquor) F in the fixing tank 2 chemically reacts with the chemical B such that a crystal is deposited in the introduction pipe 12B, disadvantageously clogging the inlet of the pipe 12B and thereby varying the mixing ratio of the chemicals A and B. Actually, due to gas generated by the fixing solution F, a crystal is deposited in the pipe 12B even if the end of the introduction pipe 12B is not in contact with the surface of the fixing solution. There are two reasons for such crystal deposition, as follows:
(1) Chemical reaction between chemicals A and B:
The principal component of the chemical A, i.e., thiosulfate, is generally not stable for acid. Each of a dilute ratio of the chemical A, the chemical B, and water C to the fixing solution F is set to a concentration slightly lower than a limit (approximately pH4) at which thiosulfate is decomposed. Thus, sulfur is produced by the following reaction when the chemical A is in contact with the chemical B. Na.sub.2 S.sub.2 O.sub.3 +2CH.sub.3 COOH.fwdarw.2CH.sub.3 COONa+H.sub.2 O+SO.sub.2 .uparw.+S.dwnarw.
(2) Contact with air:
The components in the chemicals are precipitated by water evaporation in air.